1. Field of the Invention
This invention relates to a process for manufacturing semiconductor devices and more particularly to an improved step-and-repeat method of exposing arrays of patterns in the formation of components of integrated circuit semiconductor devices.
2. Description of Related Art
U.S. Pat. No. 5,563,012 of Neisser for xe2x80x9cMulti Mask Method for Selective Mask Feature Enhancementxe2x80x9d describes a method for forming a mask by dividing or grouping pattern shapes into shape groups according to feature types. Two or more overlay masks can contain complementary pattern shapes which are employed sequentially. As stated at Col. 3, lines 46-48, xe2x80x9cThus the entire pattern of the original mask is printed by successive of the overlay mask patterns on to the photoresist.xe2x80x9d This requires removing a mask and substituting one or more complementary masks for the original mask.
U.S. Pat. No. 5,308,741 of Kemp for xe2x80x9cLithographic Method Using Double Exposure Techniques, Mask Position Shifting and Light Phase Shiftingxe2x80x9d describes a method of xe2x80x9cusing double exposures, physical mask shifting and light phase shifting to form masking features on a substrate masking layer. A first Phase Shifting Mask (PSM) is used to form at least one image by exposing a mask at a first location. A second exposure is made using either a second PSM or reusing the first PSM. The PSM used in the second exposure is positioned to partially overlap the original position of the first PSM. If the first PSM is reused, it is shifted to a second exposure position. In either case, in the second exposure the regions of the substrate with first and second exposures have some common unexposed regions which are used to form the masking features. If the first mask is reused it can be shifted by a rectilinear or rotational displacement into the second position. After removal of the exposed resist there are a plurality of unexposed regions on the substrate.
U.S. Pat. No. 5,815,245 of Thomas et al. for xe2x80x9cScanning Lithography System with Opposing Motionxe2x80x9d describes a scanning photolithography system which uses opposing motion of a reticle and a blank to compensate for image reversal by a projection system such as a conventional Wynne-Dyson optical system which forms a reverted image on a blank. During scanning the reticle moves in a direction opposite to the direction in which the blank moves. Linear motors are used. See Col. 14, lines 16-20, where it is stated xe2x80x9cTypically, relative motion is provided by a microstepper or other precision motor driving the secondary stage under control of a conventional control mechanism receiving feedback from the reticle alignment system.xe2x80x9d
In accordance with this invention a method and a system are provided for exposing a workpiece in a dual exposure step-and-repeat process starts by forming a design for a reticle mask. Deconstruct the design for the reticle mask by removing a set(s) of the features that are juxtaposed. Form unexposed resist on the workpiece. Load the workpiece into a stepper. Load the reticle mask into the stepper. Expose the workpiece through the reticle mask. Reposition the workpiece by a nanostep. Then expose the workpiece through the reticle mask after the repositioning. Test whether the plural exposure process is finished. If the result of the test NO the process loops back to repeat the process. Otherwise the process has been completed. An overlay mark is produced by plural exposures of a single mark. A dead zone is provided surrounding an array region in which printing occurs subsequent to exposure in an original exposure. Stepper-framing-blades are moved over the dead zone to prevent additional exposure.
Alternatively, the workpiece can be fully exposed first by stepping a series of full steps from the start position to the end of the area to be exposed. Then go back to the starting position. Then make a nanostep to reset the starting position. At that point re-expose from the reset starting position in the same way with a series of full steps from the reset starting position which carries the nanostep offset forward.